This invention pertains to temperature compensation devices and methods and particularly to temperature compensation for optical devices.
The performance of many devices is sensitive to changes in size of the device or a constituent part. However, with many materials, changes of temperature generally cause the material to change in size because the material has a non-zero Coefficient of Thermal Expansion (CTE). The CTE is a measure of the change in size of a material as a function of temperature and is defined, in English units, as the change in xe2x80x9cinches per inch per degree Fahrenheit.xe2x80x9d One such device where performance is effected by temperature is a simple scale. The accuracy of the scale depends on fixed spacing of the regular marks over an operating temperature.
Various methods and devices are known in the art to compensate for temperature induced thermal expansion. For example, U.S. Pat. No. 5,095,632, xe2x80x9cComposite Structure Unidirectionally Stable With Respect to Thermal and Moisture Expansion,xe2x80x9d discloses the use of multiple materials with different CTE""s for thermal compensation in a scale. Other known thermal compensation methods are applicable to devices that operate by the action of electromagnetic wave phenomena and which may also be very sensitive to thermal expansion and contraction. U.S. Pat. No. 4,287,495, xe2x80x9cThermally Compensated Phase-Stable Waveguide,xe2x80x9d discloses the use of materials with differing and compensating CTE""s to control the size, and thus the phase properties, of a waveguide for radio-frequency or microwave radiation. A device for coupling two optical waveguides with temperature compensation is shown in U.S. Patent No. 5,416,867, xe2x80x9cPassive Temperature-Compensated Optical Waveguide Coupler.xe2x80x9d Methods of precisely maintaining the position of optical lenses over a significant temperature range are disclosed in U.S. Pat. No. 5,523,893, xe2x80x9cStrain-Free Temperature Compensated Optical Mounts,xe2x80x9d and in U.S. Pat. No. 5,557,474, xe2x80x9cPassive Thermal Compensation Method and Apparatus.xe2x80x9d
In one aspect of the invention, a method and an apparatus are disclosed for mounting a temperature-sensitive device to a bi-material thermostatic structure in such a manner that the thermostatic structure changes its curvature in a complementary response to temperature-induced size changes of a temperature sensitive device. The bi-material thermostatic structure applies a force in opposition to the temperature induced change of the temperature-sensitive device. In a second aspect, and a preferred embodiment of the invention, the method of the invention is applied to thermal compensation of optical fiber refractive index gratings, which are used as components in wave division multiplexed (WDM) fiber optic communications systems.